The disposal of large quantities of high level radioactive wastes generated in the reprocessing of spent power reactor fuel is a problem of considerable importance to the utilization of nuclear power. It is generally accepted that the most promising approach is to convert these radioactive wastes to a dry solid form which would render such wastes chemically, thermally and radiolytically stable. This problem of dry solid stability is closely related to the safety of human life on earth for a period of over 20,000 years. For example, radioactive waste contains the isotopes Sr.sup.90, Pu.sup.240, and Cs.sup.137 whose half lives are 29 years, 66,000 years, and 30 years respectively. These isotopes alone pose a significant threat to life and must be put into a dry, solid form which are stable for thousands of years. The solid radioactive waste form must be able to keep the radioactive isotopes immobilized for this length of time, preferably even in the presence of a water environment.
A process for fixating radioactive materials in a dry solids form having high resistance to leaching and other forms of chemical attack would not only be suitable for the disposal of radioactive nuclear wastes, but also for the fabrication of radioactive sources useful in industry, medicine, and in the laboratory.
There does not presently exist any practical, fool-proof means for the safe disposal, storage and immobilization of pernicious radioactive waste material. Present day storage containers do not provide sufficient isolation and immobilization of such radioactive material, sufficient long-term resistance to chemical attack by the surroundings, and sufficient stability at high temperature.
One present route is the so-called dry solids approach which involves the method of fixation of waste materials in glasses via melting glass procedures. This approach offers some improvement regarding isolation and decrease in the rate of release of radioactive elements when the outer envelopes or containers are destroyed. Further, glasses remain relatively more stable at high temperatures than plastics and are generally more chemically durable in saline solutions than are metals. Glasses with high chemical durability and low alkali ion conductivities are melted at very high temperatures, e.g., 1800.degree. C. and higher. Such high melting processes are economically unsound and moreover, cause a dangerous problem due to the volatilization of pernicious radioactive materials. In view of the overall difficulty of handling radioactive material, and especially in view of the danger of volatilization of radioactive material into the atmosphere, attention was directed to using glasses having relatively low melting temperatures, that is to say, using glasses with SiO.sub.2 content as low as 27 weight percent. While the problem of volatilization of radioactive materials was reduced, it was not completely controlled. Moreover, the resultant glass composition exhibited greatly reduced chemical durability and increased ion diffusion rates for the radioactive materials present therein. The greater this diffusion rate, the lower is the ability of the glass to keep the radioactive materials immobilized in its matrix. For long-term containment of radioactive waste, demanded under present day standards, these glass compositions were inadequate. Additionally, none or very small amounts of gaseous radioactive materials are trapped by the foregoing procedures.
As will be apparent hereinafter from the various aspects of applicants' contributions to the art, there are provided novel methods to obtain novel compositions and articles for the containment of pernicious and dangerous radioactive material over extraordinarily long periods of time. Unlike melting glass containment procedures, the methods of the invention need not involve any steps which would expose radioactive material to temperatures above about 900.degree. C. thereby eliminating the environmental hazard due to volatilization of radioactive material into the atmosphere. In addition, there are provided novel methods for the fixation and immobilization of radioactive gas wastes such as Kr. I, Xe, Ra, etc., in a glass matrix.